This invention relates to electrostatically-enhanced thin-film condensing gas-to-liquid heat exchangers in dehumidifying applications, and especially to their use for condensing potable water from humid atmospheric air in advance of natural precipitation. The invention includes means for substantially increasing condensate product yield, wherein humid atmospheric air is passed through a heat transfer section enveloped by an electromagnetic field. The invention also relates to separation of other condensable vapors from gaseous mixtures passing through ionizing heat exchanger apparatuses, where molecules of the condensable vapor have polar characteristics.
Natural rainfall is generally recognized as the precipitation of liquid drops of water released by condensing heat transfer, which occurs when warm moisture-bearing air masses are cooled by turbulent or convective mixing with colder air masses. Virtually all atmospheric moisture is thought to have originated from and been released by the evaporative solar heating of ocean waters. Water evaporated from ocean surfaces mixes with adjacent moving warm air masses, and is carried aloft by turbulence or convective air currents. Other atmospheric air currents derived from the earth's rotation, thermal effects of cyclic solar heating and fluid friction between the interfaces of moving air streams cause the movement of cool air masses away from colder regions of the earth's surface. The natural condensing process caused by the random mixing of cold air masses with moisture-bearing warm air masses is the principal mechanism of atmospheric precipitation, upon which much of life depends.
Usefulness of available land areas for sustaining plant and animal life is substantially limited by the random availability of natural precipitation. Many areas of the earth are plagued by drought, even when the local atmosphere may be relatively humid.
Air at any given temperature contains a limited amount of water vapor, which is a maximum at the saturation or dew point temperature. The water-vapor content or capacity of atmospheric air increases with rising temperature, and decreases as the air temperature falls. During the evening following a warm day, air that is nearly saturated with water vapor cools until it drops below the saturation temperature. As the air continues to cool, water vapor will condense onto any nearby cool surface as the air temperature drops below the dew point temperature, until a new saturation temperature is reached for the air-water vapor mixture.
The formation of single raindrops from the water vapors of clouds is only partly understood at this writing. Vapor condensation within clouds is commonly thought to develop by a nucleating process, when vapors condense onto available nucleating sites, such as surfaces of suspended particulates or moisture droplets. Intensive efforts by others to stimulate the release of atmospheric moisture into areas having deficient rainfall by dispersing chemical seed substances within clouds have had only limited success.
Dehumidification is a process for removing moisture from air or other gaseous fluids. A minor dehumidification of atmospheric air commonly occurs during the operation of air conditioning apparatuses, when an air stream is cooled below the dew point temperature of its water-vapor fraction. Condensation of atmospheric moisture onto the outer surfaces of exposed piping which carries a moving stream of water colder than the surrounding still air is a common phenomenon. The natural condensing process which precipitates atmospheric moisture to earth as rain, snow or sleet is but another form of dehumidification.
Dehumidification by cooling is commonly practiced in the arts related to comfort air conditioning. Typical air conditioning system operation requires that half or more of the cooling energy load be used to sensibly cool a moving mass of air and water vapor at a constant specific humidity, before any condensation of water vapor may commence. The moving mass of air and water vapor is further cooled and water vapor is removed from the air by condensing heat transfer surfaces, until a desired specific humidity is achieved. The moving mass of air and water vapor at the desired specific humidity must often be reheated to a desired temperature, before its discharge into an occupied space. An important purpose of this invention is to provide dehumidifying means which can substantially decrease the cooling energy and heating energy loads of air conditioning systems.
Condensation of diffuse vapors from large volume gaseous streams ordinarily requires that the entire gaseous stream be cooled below the saturation temperature for the partial pressure of the condensable vapor fraction. The economic separation of diffuse condensable vapors from large volume gaseous streams with substantially reduced energy requirements is an important goal of this invention, especially where molecules of the condensable vapor fraction have polar characteristics.
The invention may be used to dehumidify and extract potable water from atmospheric air in areas where an adequate supply of cooling water is unavailable. Such usage requires development of economical new cyclic means for rejecting absorbed heat from the condenser tubes of the heat exchanger apparatuses. The successful development of dehumidifying heat exchanger apparatuses having self-contained cyclic means of heat rejection would free mankind from its historic dependence on the random availability of water derived from the processes of natural precipitation.
While the apparatuses of the invention are largely described in connection with electrostatically-enhanced thin-film condensation of atmospheric water vapor onto cooler surfaces of heat transfer conduits within a heat exchanger enclosure, it will be understood by those skilled in the heat exchanger arts that variations of the condensing heat transfer apparatuses and methods described hereinafter may be employed advantageously in the design of other related electrostatically-enhanced heat exchanger apparatuses without departing from the scope of the invention.
As used herein:
The term `fluid` shall refer to any liquid or gaseous medium. PA0 The term `single-pass` shall relate to a one directional passage of a fluid stream through a heat exchanger. PA0 The term `wick` shall apply to an elongate woven fibrous braid or other absorvent cellular composition which absorbs and transfers liquid from one point to another by means of capillary attraction or by hydrostatic pressure effects. PA0 The term `wicking distance` shall refer to the projected vertical distance between higher and lower levels of a wicking system ower which hydrostatic pressure effects complement the forces of capillary attraction to accelerate the internal drainage of absorbed liquids. PA0 The term `electrostatic enhancement` shall relate to a system of charged electrodes disposed between heat transfer conduits of a heat exchanger which electrostatically impels condensate onto surfaces of the heat transfer conduits. PA0 The term `thin-film` shall apply to a concentrated fluid film adjacent the surface of a heat transfer conduit. PA0 The term `electromagnetic field` shall refer to lines of force emanating from a ferromagnetic body enveloped by an electric coil, when an electrical current flows through the coil.
The primary object of the invention is to develop improved heat exchanger configurations which economically separate and condense water vapors from a humid air stream passing through a heat exchanger.
Another important object is to provide means for concentrating diffuse water vapors onto condensing heat transfer conduits as a humid atmospheric air stream passes through a heat exchanger.
An additional object is to provide means for enhancing the formation of liquid droplets from water vapors, within an atmospheric air stream passing through a heat exchanger.
A further object is to develop electromagnetic means which physically impel water vapor molecules onto condensing surfaces of a heat exchanger, while polar axes of the water vapor molecules are electrostatically oriented between charged electrodes and grounded heat transfer conduits.
Yet another object is to develop heat exchanger means which may condense and separate other condensable vapors from large volume gaseous streams.
With the foregoing objects in view, together with others which will appear as the description proceeds, the invention resides in the novel assembly and arrangement of cooperating gas-to-liquid condensing heat exchanger elements, cooling means, ionizing and electromagnetic means which will be described fully in the specification, illustrated in the drawings, and defined in the claims.